Aron @ Shell Bell
Evs: Doesnt matter
Nature: Doesnt matter
You need a sandstorm though. So have some one set that up for this pokemon
Counters:Any Steel,Rock,Ground or Ghost types.
I dont know why you changed it from Aron to Donphan and basically the rest of the question.But heres Donphan.
Evs: Dont matter
Nature: Dont matter
Endeavor to bring to 1 HP then Ice Shard for the Priority Kill.
Entry hazards can be a problem for both of these guys(Thanks LadySerperior)